A wireless power transfer system has been known as a device for transmitting power. The wireless power transfer system is a power feeding system using electromagnetic induction or magnetic resonance by a coil, etc. This system transmits power from a power transmitter to a power receiver which is not in direct contact with the power transmitter. For example, this system is applied to a system for charging a movable object that uses electricity as an energy source such as an electric vehicle or a plug-in hybrid vehicle. In such a charging system, the power receiver is attached to a chassis, etc. of the electric vehicle, and the power transmitter is disposed below the vehicle.
A technology described in Patent Literature 1 is known as a coil device used for the wireless power transfer system. This coil device has a plurality of substrates provided with a coil conductor wound in a helical shape. The substrates are stacked in a thickness direction thereof. Further, the coil conductor is regarded as one conductor.